Nicotine treatment decreases food intake and body weight via a leptin-independent pathway in Psammomys obesus

It has been reported previously that leptin may be involved in nicotine\u27s ability to reduce body weight. Our aim was to investigate whether the anorexic action of nicotine is related to the actions of leptin by utilizing lean leptin-sensitive and obese leptin-resistant Psammomys obesus. Lean and obese P. obesus were assigned to receive nicotine sulphate at 6, 9 or 12 mg/day or saline (control) for 9 days (n = 6-10 in each group), administered using mini-osmotic pumps. Food intake, body weight, plasma leptin concentrations, plasma insulin and blood glucose were measured at baseline and throughout the study period. Nicotine treatment reduced food intake by up to 40% in lean and obese P. obesus. Plasma leptin levels fell significantly only in lean nicotine-treated animals, whereas no changes were observed in obese nicotine-treated animals. However, both lean and obese nicotine-treated animals had similar reductions in body weight. Our results show that nicotine has dramatic effects on food intake and body weight, however, these changes appear to be independent of the leptin signalling pathway.<br /

Reduced-Complexity Maximum-Likelihood Detection in Downlink SDMA Systems

The literature of up-link SDMA systems is rich, but at the time of writing there is a paucity of information on the employment of SDMA techniques in the down-link. Hence, in this paper a Space Division Multiple Access (SDMA) down-link (DL) multi-user communication system invoking a novel low-complexity Maximum Likelihood (ML) space-time detection technique is proposed, which can be regarded as an advanced extension of the Complex Sphere Decoder (CSD). We demonstrate that as opposed to the previously published variants of the CSD, the proposed technique may be employed for obtaining a high effective throughput in the so-called “over-loaded” scenario, where the number of transmit antennas exceeds that of the receive antennas. The proposed method achieves the optimum performance of the ML detector even in heavily over-loaded scenarios, while the associated computational complexity is only moderately increased. As an illustrative example, the required Eb/N0 increased from 2 dB to 9 dB, when increasing the normalized system load from unity, representing the fully loaded system, to a normalized load of 1.556

Measurement of the Nodal Precession of WASP-33 b via Doppler Tomography

We have analyzed new and archival time series spectra taken six years apart during transits of the hot Jupiter WASP-33 b, and spectroscopically resolved the line profile perturbation caused by the Rossiter-McLaughlin effect. The motion of this line profile perturbation is determined by the path of the planet across the stellar disk, which we show to have changed between the two epochs due to nodal precession of the planetary orbit. We measured rates of change of the impact parameter and the sky-projected spin-orbit misalignment of $db/dt=-0.0228_{-0.0018}^{+0.0050}$ yr$^{-1}$ and $d\lambda/dt=-0.487_{-0.076}^{+0.089}$~$^{\circ}$ yr$^{-1}$, respectively, corresponding to a rate of nodal precession of $d\Omega/dt=0.373_{-0.083}^{+0.031}$~$^{\circ}$ yr$^{-1}$. This is only the second measurement of nodal precession for a confirmed exoplanet transiting a single star. Finally, we used the rate of precession to set limits on the stellar gravitational quadrupole moment of $9.4\times10^{-5}<J_2<6.1\times10^{-4}$.Comment: Published in ApJL. 5 pages, 3 figures. Corrected error in the calculation of J_

Do anomalously-dense hot Jupiters orbit stealth binary stars?

Funding: ACC and TGW acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1.The Wide Angle Search for Planets (WASP) survey used transit photometry to discover nearly 200 gas-giant exoplanets and derive their planetary and stellar parameters. Reliable determination of the planetary density depends on accurate measurement of the planet’s radius, obtained from the transit depth and photodynamical determination of the stellar radius. The stellar density, and hence the stellar radius are typically determined in a model-independent way from the star’s reflex orbital acceleration and the transit profile. Additional flux coming from the system due to a bright, undetected stellar binary companion can, however, potentially dilute the transit curve and radial velocity signal, leading to under-estimation of the planet’s mass and radius, and to overestimation of the planet’s density. In this study, we cross-check the published radii of all the WASP planet host stars, determined from their transit profiles and radial-velocity curves, against radiometric measurements of stellar radii derived from their angular diameters (via the Infrared Flux method) and trigonometric parallaxes. We identify eight systems showing radiometric stellar radii significantly greater than their published photodynamical values: WASPs 20, 85, 86, 103, 105, 129,144 and 171. We investigate these systems in more detail to establish plausible ranges of angular and radial-velocity separations within which such “stealth binaries” could evade detection, and deduce their likely orbital periods, mass ratios, and flux ratios. After accounting for the dilution of transit depth and radial velocity amplitude, we find that on average, the planetary densities for the identified stealth binary systems should be reduced by a factor of 1.3.Peer reviewe

Dynamical mass determination and partial eclipses of the heartbeat star HD 181793

Funding: ACC and TGW acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1.We identify the bright Am-type star HD 181793 to be a previously-unknown eclipsing, chemically peculiar heartbeat binary, the second of its kind known. The system carries an orbital period of P = 11.47578275 ± 0.00000055 days. We use TESS photometry and LCOGT NRES radial velocity data to build a self-consistent orbital model and determine the fundamental stellar characteristics of the primary. We use a spectral separation method to unveil the secondary and measure the masses of both stars. The radial velocity amplitude of the primary, K1 = 47.41+0.13-0.12 km s-1, gives a mass M1 = 1.57 ± 0.01 M⊙. The secondary radial velocity amplitude K2 = 84.95+0.12-0.09 km s-1 yields a mass ratio $q = 0.558 ± 0.002$ and a secondary mass M2 = 0.87 ± 0.01 M⊙. From the spectral energy distribution and Gaia parallax we find a radius R1 = 2.04 ± 0.05 R⊙. The grazing transit profile and spectroscopic luminosity ratio indicate R2 = 1.04+0.15-0.10 R⊙, suggesting an early-K spectral type. We show that the heartbeat feature in the TESS light curve can be explained by time-varying ellipsoidal variation, driven by the orbital eccentricity of e = 0.3056+0.0024-0.0026, and relativistic beaming of the light of the primary. We find no evidence of tidally-excited oscillations.Peer reviewe

A New Method for Estimating the Distance to Young Open Clusters

We present a new technique for estimating the distance to young open clusters. The method requires accurate measurement of the axial rotation period of late-type members of the cluster: rotation periods are first combined with projected rotation velocities and an estimate of the angular diameter for each star -- obtained using the Barnes-Evans relation between colour and surface brightness. A 'best' cluster distance estimate is then determined using standard techniques from the theory of order statistics which are in common use in the general statistics literature. It is hoped that this new method will prove a useful adjoint to more traditional distance methods, and will provide a better %determination of the distance scale within the solar neighbourhood. (Figures / preprint available on request)Comment: Plain Latex version 3.1, 14 pages, Sussex-AST-93/8-1, to appear in MNRA

Slingshot prominences : nature’s wind gauges

We acknowledge funding from the Science and Technology Facilities Council consolidated grant ST/R000824/1Mass-loss rates for the tenuous, hot winds of cool stars are extremely difficult to measure, yet they are a crucial ingredient in the stars’ rotational evolution. We present a new method for measuring these mass-loss rates in young, rapidly rotating stars. These stars are known to support systems of ‘slingshot prominences’ fed by hot wind material flowing up from the stellar surface into the summits of closed magnetic loop structures. The material gathers and cools near the co-rotation radius until its density becomes large enough that it is visible as a transient absorption feature in the hydrogen Balmer lines and strong resonance lines such as Ca ii H & K. Here we present the key insight that the sonic point usually lies well below the condensation region. The flow at the wind base is therefore unaffected by the presence of an overlying prominence, so we can use the observed masses and recurrence times of the condensations to estimate the mass flux in the wind. These measurements extend the relationship between mass-loss rate per unit surface area and X-ray flux to span 5 orders of magnitude. They demonstrate no evidence of the suspected weakening of stellar mass-loss rates at high X-ray flux levels.Publisher PDFPeer reviewe

A Kepler study of starspot lifetimes with respect to light-curve amplitude and spectral type

ACC acknowledges support from STFC consolidated grant number ST/M001296/1. RDH gratefully acknowledges support from STFC studentship grant ST/J500744/1, a grant from the John Templeton Foundation, and NASA XRP grant NNX15AC90G.Wide-field high-precision photometric surveys such as Kepler have produced reams of data suitable for investigating stellar magnetic activity of cooler stars. Starspot activity produces quasi-sinusoidal light curves whose phase and amplitude vary as active regions grow and decay over time. Here we investigate, first, whether there is a correlation between the size of starspots - assumed to be related to the amplitude of the sinusoid - and their decay time-scale and, secondly, whether any such correlation depends on the stellar effective temperature. To determine this, we computed the auto-correlation functions of the light curves of samples of stars from Kepler and fitted them with apodised periodic functions. The light-curve amplitudes,representing spot size, were measured from the root-mean-squared scatter of the normalized light curves. We used a Monte Carlo Markov Chain to measure the periods and decay time-scales of the light curves. The results show a correlation between the decay time of starspots and their inferred size. The decay time also depends strongly on the temperature of the star. Cooler stars have spots that last much longer, in particular for stars with longer rotational periods. This is consistent with current theories of diffusive mechanisms causing starspot decay. We also find that the Sun is not unusually quiet for its spectral type -stars with solar-type rotation periods and temperatures tend to have(comparatively) smaller starspots than stars with mid-G or later spectral types.Publisher PDFPeer reviewe

X-ray Emission From Nearby M-dwarfs: the Super-saturation Phenomenon

A rotation rate and X-ray luminosity analysis is presented for rapidly rotating single and binary M-dwarf systems. X-ray luminosities for the majority of both single & binary M-dwarf systems with periods below $\simeq 5-6$ days (equatorial velocities, V$_{eq}>$ 6 km~s$^{-1}$) are consistent with the current rotation-activity paradigm, and appear to saturate at about $10^{-3}$ of the stellar bolometric luminosity. The single M-dwarf data show tentative evidence for the super-saturation phenomenon observed in some ultra-fast rotating ($>$ 100 km~s$^{-1}$) G & K-dwarfs in the IC 2391, IC 2602 and Alpha Persei clusters. The IC 2391 M star VXR60b is the least X-ray active and most rapidly rotating of the short period (P$_{rot}<$ 2 days) stars considered herein, with a period of 0.212 days and an X-ray activity level about 1.5 sigma below the mean X-ray emission level for most of the single M-dwarf sample. For this star, and possibly one other, we cautiously believe that we have identified the first evidence of super-saturation in M-dwarfs. If we are wrong, we demonstrate that only M-dwarfs rotating close to their break up velocities are likely to exhibit the super-saturation effect at X-ray wavelengths.Comment: 12 pages, 4 figures, accepted by MNRA

Spin-orbit angles: A probe to evolution

We will present our campaign to estimate the projected spin-orbit angle for transiting hot Jupiters, obtained via observations of the Rossiter-McLaughlin effect. Combining our results to those of other teams we show what the current distribution in projected spin-orbit angle is, quickly reminding what interpretation we make of it. Finally we will show early results from a campaign that we initiated, surveying the Rossiter-McLaughlin effect on transiting SB1 intended to provide a comparison sample to the transiting planet's result